As more and more communication is performed in wireless/cellular communication systems, the requirements on such systems are constantly increasing. Such requirements relate both to increased coverage and support of higher data rates, or preferably a combination of both.
To enhance coverage and data rate a forwarding node, such as a repeater or a relay, is often used. Such forwarding nodes typically receive the signal and amplify it before transmitting it to the receiver. The benefit of using repeaters and relays stems primarily from that splitting a long distance in two hops allows increased data rate on each link as well as End-To-End total data rate.
The distinction between the repeaters and relays is not entirely clear cut. Often, the term repeater is used to denote a simple, low processing node that receives a signal, amplifies it and sends it out. However, some repeaters also demodulate and remodulate the received signal, and even include power control. A relay is normally considered a bit more advanced and complex. It typically receives a signals demodulated and (FEC)-decode it prior deciding which resource to send it onto, e.g. through scheduling. To complicate things a bit, relaying is often used as an umbrella term, including any node forwarding any piece of information.
There are many different types of repeaters, such as frequency translating and on-frequency repeaters. The so called on-frequency repeater transmits the signal on the same resource as it was received on. That is, it uses the same frequency and/or coding scheme and transmits the signal immediately upon receiving it. Such a repeater avoids the resulting throughput loss, often referred to as a duplex loss, that arises in many schemes where the node forwarding data or signal can not receive and transmit at the same time and on the same frequency.
On the other hand, an on-frequency repeater is prone to self-interference since the same signal is received and transmitted at virtually the same time. Therefore, the gain that can be applied in such a repeater is limited to a level that will not cause excessive self-interference. To minimize self-interference, a high degree of isolation between the input antenna and the output antenna is usually aimed for. Further techniques for self-interference cancellation are often applied. The latter means that the repeater internally cancels the repeater output signal that is fed back to the repeater. Even with such measures to reduce self-interference, the maximum gain is limited.
The on-frequency repeater is an attractive solution to come to terms with the duplex loss seen for relays and frequency translating repeaters, but is often inadequate when the repeater receives a weak signal and needs to amplify the signal and communicate to a distant receiver to which the path loss is high.
On the other hand, repeaters that receive and transmit on different resources, such as frequency translating repeaters avoid self-interference at the cost of introducing a duplex loss.
Hence, when designing networks a trade-off is made between the need for high amplification gain and optimum throughput.
A network architecture using relay nodes is disclosed in Patent Application Publication No. US2007/0160014 A1. Patent Application Publication No. U.S. 2005/0232223 discusses the use of on-frequency or frequency-shifting repeaters.